Background

Black Soldier Fly (hermetia illucens) is a fly when it is grown up, but it does time as a larva before that (similar to mosquitoes etc.). These larvae are useful beasties: they chew through all kinds of organic waste and leave compost behind, similar to worms. They are a very nutritious feed for chickens, fish, and other animals. (You can even eat them yourself, unless you've let your culture bamboozle you into thinking that eating larvae is disgusting.) They are very widespread around the world in both tropical and temperate climates. There's a great website called Black Soldier Fly Blog where you can get up to speed. Here's the elegant bit: when the larvae are ready to pupate (i.e. turn into flies), their instincts tell them to crawl up and out of the compost heap. If you put a bit of thought into the design of their habitat, you can arrange things so that they crawl where you want them, maybe dropping right into your fish tank. (Permaculture teaches us to work with nature, and to place things where they are needed.)

My first colony

I wanted to farm these beasties in Haïti. We have chickens here and an aquaponics system, and I'd recently met a fish farmer who was having trouble sourcing fish feed. Loads of people are farming tilapia and chickens in the country, and another feed source, especially a free, DIY one, would be wonderful. So let's source some grubs! I looked for farmers who were using Black Soldier Fly, but I couldn't find any in the country. I researched building a special compost heap as bait for Black Soldier Flies, but it would've taken 3-4 weeks to attract them. So I took the third option: I decided to grab some in the wild. Over I go to our compost heap, spade in hand. The first thing I saw was a completely black fly buzzing near the heap. Good sign. I couldn't get a close enough look to identify it with certainty, but it looked like a Black Soldier Fly to me. I start digging in the compost heap and see all sorts of species busily decomposing things. The compost heap was full of fruit fly larvae, but eventually I found these:

I am sure these are Black Soldier Fly larvae because they are big, have segmented bodies, a pointed dark segment at one end and a flat dark segment and a few hairs at the other. Some are tiny and white, and the older they get, the darker they get.

This reinforces a point I have written about before: incredibly valuable biological resources are all around us, and it just takes a little cleverness to tap them. After spending days looking for a place I could buy or borrow them, I found them a few meters away from me in a few minutes of digging. The total cost of this project was Nothing. You don't always need to buy things; use the biological resources that are around you. After all, people did that for millions of years.

I grabbed a few larvae and put them in a bucket with food scraps. When I went to inspect the bucket the next day, a cloud of fruit flies greeted me. Most of the Black Soldier Fly larvae were dead, but I found a few still wriggling. By around day 6, it was all fruit flies and fruit fly larvae, and I couldn't find BSF still alive. Feck it. Reset. I can always get more from the compost heap.

My second colony

The second time around, I made three changes:

My online researches led me to believe that it is important to provide good drainage. I had overlooked this the first time; there was water pooling in the bottom of the bucket. So the second time I laid the bucket on its side, sloped slightly downwards for water to come out.

The evidence of my senses led me to believe that the larvae don't like to live on the surface. I'd found them deep down inside the compost heap. So, emulating this, I covered the second attempt with dry brown leaves. One of the principles of permaculture is to observe what is already happening and replicate it. I think this worked, perhaps more by discouraging the fruit flies than encouraging BSF.

I also threw in a much larger starter population of larvae, and on day 2 I went back to the compost heap and added even more.

This was more successful than the first experiment. Some fruit flies showed up, but fewer this time around. By day 8, I can't see any fruit flies or fruit fly larvae, and parts of the compost heap are visibly writhing with Black Soldier Fly activity. Time to call this a success and move these guys to a more permanent home, equipped with a euthanasia chute....

Harvester

I built this whole thing from a bucket and a plastic bottle. The only tool was a knife. It took about 20 minutes.

This is where we'll be cutting the lid. The slit at the top is for the adult females to enter and lay their eggs; the door at the bottom is where the larvae exit

Holes in the lid are cut. Now I'm gonna cut a hole a little bit above the bottom to allow water to exit.

I cut a long strip of plastic from an empty bottle. This will go inside the bucket to guide the larvae towards the exit

I cut some notches in the strip of plastic - one grabs the lip of the bucket, the other grabs the drainage hole. This guides the larvae to the exit hatch.

And cut a little bit out of the lid to allow it to close around the plastic strip, and allow the larvae to fall out.

Ta-da! This may be the first Black Soldier Fly farm in Haïti. The tray at the bottom is to catch larvae. It needs to be kept at an angle like this for two reasons: allow the drainage hole to do its job, and give the larvae a ramp to climb out of.

It worked first time! I finished building the harvester in the evening, and woke up to this the next morning. The fact that all the grubs are big and dark is a good sign; if the conditions inside the bucket were bad, we would see immature grubs escaping.

Update #1: New catchment system

I stopped seeing larvae in that white plastic tray on day 3. Did they stop coming out? Nope, my theory is that the local lizards got hip to the fact that that tray was a source of food. Pwoblèm! I set up this new catchment system; I think it should keep out larcenous lizards. I had to pierce a few small holes in the bottom of the catchment bottle so that it wouldn't fill with rainwater.

The system in the previous photo worked ok, but kept falling off, so I notched the bottle so it would hold the bucket.

Lindsay seemed disappointed she couldn't get the grubs from the bottom of the bottle.

Update #2: Covering the drainage hole

I added the bottom of a plastic jug over the drainage hole to prevent it getting clogged. I also put in a new plastic strip to guide the grubs to the exit. I wasn't entirely happy with the initial design of the plastic strip, because if the larvae had followed it downhill, it would have guided them out the drainage hole. This way, one end is at the exit, and the other end is at the drain cover. If they follow it uphill, they'll fall into my harvest bottle, and if they follow it downhill, they'll still be in the compost bucket.

Update #3: Catchment system version 3

The lizard-proof catchment system with two bottles kept falling over, so I made a simpler system by cutting these notches into a plastic bottle.

The new catchment in place. The bottle won't fall off easily because the notches are cut so deep. The angle I cut the notches at allows it to stand more-or-less upright while gripping the slanted bottle. The larvae should drop nearly vertically, and have no chance of climbing out.

Update #4: Hardcore predator protexion

The bucket was full of healthy-looking larvae, but I wasn't getting them in the bottle. There are two explanations: either the layout of the bucket is wrong and the mature larvae don't find my exit, or else predators are nabbing them. We have lots of small lizards around here that could possibly be climbing inside the bucket to eat the larvae. I've also seen a rat hanging around the bucket. So I used wires to suspend it in mid-air. I can't imagine any lizard or rat climbing along a wire to get the larvae.

Update #5: Just add water

Even after hanging it up away from predators, I am still not harvesting larvae. This could mean the larvae are pupating (i.e. turning into flies) inside the bucket. This happens when the bucket is too dry and there are too many air pockets in there.
I poured a lot of water into it, flooding it temporarily. The larvae are resilient and don't drown. I also squished down the organic waste, compressing it. The next day the larvae start falling into the bottle again.